Qwestrum Engineering360 · Mechanical Engineering · Maintenance Engineering
Root Cause Analysis
Root cause analysis (RCA) finds the underlying cause of failure, not just the symptom, using tools like the 5 Whys and fishbone (Ishikawa) diagram, so corrective action prevents recurrence, per maintenance-engineering texts.
Exam tip: keep SI units consistent end-to-end, write the governing relation symbolically before substituting, and sanity-check magnitude and sign.
Key formulas & points
Skim these first — then read the full notes below.
- RCA prevents recurrence — fix cause not symptom
- Document findings in maintenance history database
Topic details
Introduction
Root cause analysis prevents repeat failures by digging past symptoms to the true cause. Indian maintenance and quality courses teach structured RCA tools.
Scope in B.Tech and GATE syllabus
The 5 Whys iteratively asks "why" until the fundamental cause is reached; the Ishikawa (fishbone) diagram organises possible causes into categories (man, machine, material, method, measurement, environment). Fault-tree and Pareto analysis complement these.
Why this topic matters in practice
Effective RCA distinguishes symptoms (a hot bearing), immediate causes (no lubrication), and root causes (a failed lubrication procedure), then fixes the root. Applying the 5 Whys and categorising causes are the exam skills.
Key relations & formulas
Formulas (Indian textbook notation)
Formulas (Indian textbook notation)
Formulas (Indian textbook notation)
Formulas (Indian textbook notation)
Notation and sign conventions
Relation 1 —
Formulas (Indian textbook notation)
Write this relation with symbols exactly as in Maintenance Engineering — SRK Rao before substituting numbers. Examiners award partial marks for a correct setup even when arithmetic slips.
Relation 2 —
Formulas (Indian textbook notation)
Write this relation with symbols exactly as in Maintenance Engineering — SRK Rao before substituting numbers. Examiners award partial marks for a correct setup even when arithmetic slips.
Relation 3 —
Formulas (Indian textbook notation)
Write this relation with symbols exactly as in Maintenance Engineering — SRK Rao before substituting numbers. Examiners award partial marks for a correct setup even when arithmetic slips.
Relation 4 —
Formulas (Indian textbook notation)
Write this relation with symbols exactly as in Maintenance Engineering — SRK Rao before substituting numbers. Examiners award partial marks for a correct setup even when arithmetic slips.
Fundamentals and definitions
RCA is disciplined problem solving: it treats a failure as evidence of a deeper deficiency and seeks the cause whose correction prevents recurrence, rather than merely repairing the symptom.
Governing relations in practice
The 5 Whys technique asks "why" repeatedly, each answer probing deeper: a broken belt → why? overheated → why? misaligned pulley → why? no alignment check → why? procedure missing — the root cause is the missing procedure, so the fix is procedural, not just a new belt.
Design and analysis considerations
The fishbone (Ishikawa) diagram structures brainstorming of potential causes into standard categories, ensuring no cause type is overlooked; fault-tree analysis works top-down through logic gates for complex failures; Pareto analysis focuses effort on the vital few causes.
Advanced theory and extensions
Good RCA separates symptom, immediate cause, and root cause, verifies the cause with evidence, and implements corrective and preventive actions. It closes the loop by confirming the failure does not recur — the ultimate test examiners emphasise.
Assumptions and validity limits
State assumptions explicitly before using any relation for root cause analysis — steady state, uniform properties, linear elastic material, ideal gas, incompressible flow, etc., as applicable.
Wrong assumptions invalidate the entire solution even when the formula is correct. In Maintenance Engineering viva and GATE descriptive questions, listing valid assumptions often earns separate marks.
Step-by-step problem approach
1. Read the question and list given data with SI units (common in Maintenance Engineering papers).
2. Draw a neat labelled diagram where applicable — examiners in Indian universities award diagram marks even when arithmetic slips.
3. Identify which relation from this topic applies to root cause analysis.
4. Use equation 1:
5. Use equation 2:
6. Substitute values, compute, and verify units and sign (direction).
7. State conclusion in one line — e.g. safe/unsafe, stable/unstable, feasible/infeasible.
2. Draw a neat labelled diagram where applicable — examiners in Indian universities award diagram marks even when arithmetic slips.
3. Identify which relation from this topic applies to root cause analysis.
4. Use equation 1:
.
5. Use equation 2:
.
6. Substitute values, compute, and verify units and sign (direction).
7. State conclusion in one line — e.g. safe/unsafe, stable/unstable, feasible/infeasible.
Applications & exam relevance
Root Cause Analysis appears in process plants and utilities. In Indian mechanical curricula this topic is tested because it connects theory to reliability and upkeep of plant equipment.
GATE and semester exams often combine root cause analysis with earlier units — revise prerequisites before attempting mixed problems.
Industry interview panels sometimes ask: "Where did you use root cause analysis?" — answer with a lab, mini-project, or plant visit example if possible.
Common mistakes in exams
• Stopping at the symptom or immediate cause rather than the root cause
• Applying the 5 Whys mechanically without evidence for each answer
• Confusing correlation with causation in cause identification
• Failing to verify that corrective action actually prevents recurrence
• Applying the 5 Whys mechanically without evidence for each answer
• Confusing correlation with causation in cause identification
• Failing to verify that corrective action actually prevents recurrence
Quick revision checklist
Before attempting root cause analysis problems, confirm you can:
1. RCA prevents recurrence — fix cause not symptom
2.
3. Document findings in maintenance history database
2.
3. Document findings in maintenance history database
Revise the solved examples in Maintenance Engineering — SRK Rao and one previous-year GATE or university paper for this unit.
Worked examples
Try the problem first — open the solution when you are ready to check.
5 Whys analysis
Problem
A pump repeatedly fails. Apply the 5 Whys to reach a plausible root cause.
Solution
Pump fails → bearing seized → no lubrication → grease line blocked → no inspection schedule → (root) missing PM procedure. Fix: institute a lubrication-inspection procedure, not just replace the bearing.
Conceptual check — Root Cause Analysis
Problem
In a Maintenance Engineering semester or GATE paper you are asked: "State the main assumption, the governing relation, and one practical consequence of root cause analysis." What should a complete answer include?
Practice questions
Most-asked interview and GATE questions for this topic — expand any item for a model answer.
- 1What is Root Cause Analysis, and why does it appear in B.Tech / GATE syllabi?
Model answer
Root cause analysis (RCA) finds the underlying cause of failure, not just the symptom, using tools like the 5 Whys and fishbone (Ishikawa) diagram, so corrective action prevents recurrence, per maintenance-engineering texts. - 2State the relation 5 Whys: iterative why until root cause found and name each symbol.
Model answer
The governing relation is . Write every symbol with SI units before substituting numbers. - 3State the relation Ishikawa and name each symbol.
Model answer
The governing relation is . Write every symbol with SI units before substituting numbers. - 4State the relation FTA: top event probability from AND/OR gate logic and name each symbol.
Model answer
The governing relation is . Write every symbol with SI units before substituting numbers. - 5State the relation Pareto: 80% failures from 20% causes and name each symbol.
Model answer
The governing relation is . Write every symbol with SI units before substituting numbers. - 6Explain: RCA prevents recurrence — fix cause not symptom
Model answer
RCA prevents recurrence — fix cause not symptom — state the assumption range and one exam trap linked to this point. - 7Explain: Failure modes: FMEA ranks RPN = S × O × D
Model answer
— state the assumption range and one exam trap linked to this point. - 8Explain: Document findings in maintenance history database
Model answer
Document findings in maintenance history database — state the assumption range and one exam trap linked to this point. - 9How would you correct this error in a viva: Stopping at the symptom or immediate cause rather than the root cause?
Model answer
Identify the wrong assumption or unit mix-up, rewrite the correct relation, and recompute with a one-line sanity check. - 10How would you correct this error in a viva: Applying the 5 Whys mechanically without evidence for each answer?
Model answer
Identify the wrong assumption or unit mix-up, rewrite the correct relation, and recompute with a one-line sanity check. - 11How would you correct this error in a viva: Confusing correlation with causation in cause identification?
Model answer
Identify the wrong assumption or unit mix-up, rewrite the correct relation, and recompute with a one-line sanity check. - 12How would you correct this error in a viva: Failing to verify that corrective action actually prevents recurrence?
Model answer
Identify the wrong assumption or unit mix-up, rewrite the correct relation, and recompute with a one-line sanity check.
Exams & GATE
- 1SRK Ch. 8 — distinguish immediate cause vs root cause in case studies.
- 2Avoid: Stopping at the symptom or immediate cause rather than the root cause
- 3Avoid: Applying the 5 Whys mechanically without evidence for each answer
- 4Avoid: Confusing correlation with causation in cause identification
📖 Standard books (India)
Maintenance Engineering — SRK Rao
Read: Syllabus unit
Reliability, RCM, and maintenance planning
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